Wearable devices have become widely used by consumers due to their small size and some smart functionalities. Among the wearable devices, smart watches are often seen as the most developed and the most advanced type of wearable devices on the market. While many advances have been made to improve the functionality and utility of the smart watches, one challenge faced by the smart watch R&D community is how to provide effective interaction between a user and his/her smart watch. In the case of smart phones, currently the most common interaction method is through the display of a smart phone, where a user can provide input by touching on a touch screen, which is available in most smart phones. This traditional method is, however, not very convenient in the context of a smart watch because the small display size of a typical smart watch is not suitable for effective touching and typing. Therefore, it is desirable to provide a wearable device with a more convenient interaction method.